This is a multidisciplinary, morphological and biochemical study in vivo and in vitro of melanogenesis in the oral mucosa and skin of mammals and that of the avian retinal pigment epithelium. Our aim is to discover how ultraviolet radiation influences the formation, melanization and transfer of melanosomes from melanocytes into keratinocytes. In transmission and scanning electron microscope studies we propose to investigate the ultrastructural events during stimulation with ultraviolet radiation and proceed to examine the nature of the junction of melanocytes and keratinocytes in freeze fracture preparations. Autoradiographic studies with tritiated Dopa should enable us to discover the time sequence of melanosome formation and establish the time when melanosomes are transferred into keratinocytes. We plan to estimate the tyrosinase activity of skin exposed to ultraviolet radiation by gel electrophoretic techniques. Finally, we propose to study the changes in the morphology of DNA and nuclear chromatin as a result of ultraviolet radiation. We also are planning to enhance the effect of ultraviolet radiation by psoralen and compare this with the effect of the carcinogen dimethylbenzanthracene in treatment combined with ultraviolet radiation thus gaining an insight into the etiology of melanoma.